recrystallized, have often been again disintegrated. Denudation means the removal of such disintegrated matter to a lower level. Of the many striking results due to the modern progress of geology there are hardly any more striking than those which relate to denudation. It was long ago seen that there must have been an immense amount of denudation; but until the successive formations were carefully mapped and measured, no one fully realised how great was the amount. One of the first and most remarkable memoirs ever published on this subject was that by Ramsay,[1] who in 1846 showed that in Wales from 9000 to 11,000 feet in thickness of solid rock had been stripped off large tracks of country. Perhaps the plainest evidence of great denudation is afforded by faults or cracks, which extend for many miles across certain districts, with the strata on one side raised even ten thousand feet above the corresponding strata on the opposite side; and yet there is not a vestige of this gigantic displacement visible on the surface of the
- ↑ "On the denudation of South Wales," &c., 'Memoirs of the Geological Survey of Great Britain,' vol. i., p. 297, 1846.
